1. Field of the Invention
The present invention relates to a serial-type ink jet printer and more particularly to an ink jet printer so configured that printing functions of a printing head are restored by sucking out thickened ink, dust and the like from a clogged nozzle through the use of negative pressure.
2. Description of the Related Art
A conventional serial-type ink jet printer is known wherein ink is discharged from a nozzle formed on a nozzle forming face of a printing head to perform printing.
In the conventional ink jet printer of this kind, image information covering one line is printed on paper while a printing head scans to and from once or more than one time in the direction of the width and, when the printing covering one line is terminated, it is started on a new line again by scanning in the direction of the width.
The ink jet printer can provide printed images with high quality and has an advantage that its printing head produces comparatively less noise while being printed.
However, the conventional ink jet printer presents a problem in that a nozzle of the printing head, when not in use, may get clogged up with dried ink, dust and floating materials in the air. Solidified ink, adhered dust and the like may cause defective discharging of ink (so-called "dot omission") and interfere with normal printing. To prevent this, when the nozzle is not in use, the printing head is taken off from the ink jet printer to be housed in a keeping box or a nozzle forming face of the printing head is sealed to prevent drying of ink, adherence of dust and the like. However, it is inconvenient for a user to take the printing head off from the ink jet printer and to house it in the keeping box in every use and, in many cases, such storing of the printing head in the keeping box is not put into practice accordingly.
Another method for solving the problem of clogging of the nozzle of the printing head is to provide the ink jet printer with a nozzle restoring mechanism in which printing functions of the printing head are restored by using suction processes.
The conventional nozzle restoring mechanism is so configured that caps surrounding a group of nozzles in a closed contact with a nozzle forming face of a printing head are provided and air within a sealed cap chamber formed by the cap and the nozzle forming face is sucked so that solidified ink, dust and the like within the nozzle are sucked out forcedly together with air. The nozzle restoring mechanism, unlike in the case of using the keeping box, has an advantage that there is no need for intervention of users. That is, the ink jet printer is provided with a nozzle restoring section on the side of its printing section and, when the nozzle is not in use, the printing head is automatically brought to the position of the nozzle restoring section.
However, the conventional nozzle restoring mechanism using suction processes presents a problem in that waste ink residing in the cap after the suction has been carried out (or waste ink residing within a path of ink discharged by the suction) invades backward into the nozzle by residual negative pressure within the nozzle of the printing head, causing the nozzle to be contaminated with waste ink.
The influence by the contamination remarkably shows up in a color ink jet printer in particular. Recently, users tend to prefer the color ink jet printer that can provide color printing. In response to these demands, the recent ink jet printer can use multicolor ink and is provided with a printing head with nozzles that can be operated in use with such various color ink. In such a color ink jet printer, if waste ink is present even in trace amounts, it causes a color image to be degraded. Especially, for example, if bright color ink such as yellow ink or the like is mixed with dark color ink such as black ink, the resulting color image decreases in the quality, causing a feeling of visual strangeness.
Such a malfunction caused by the mixing of ink having different components does not always occur only in ink jet color printers. For example, in the case of an ink jet printer using black ink only, the printing head with different specifications uses black ink having different components. In any case, therefore, mixing of ink must be avoided in the operation of printers.